1. Field of the Invention
The present invention relates to a machining head capable of simultaneously performing cutting and boring of a workpiece such as a cylinder head of an engine. More particularly, it relates to a guide device for a machining head capable of machining a workpiece accurately, a machine having the guide device, and a guide method.
2. Description of the Related Art
In a machine of a type having a guide bar attached to a machining head and a guide post for guiding the guide bar, a clearance formed when the guide bar is fitted in the guide post produces vibrations at the time of workpiece machining. This presents a problem in that the vibrations make it difficult to perform accurate machining, and exert a remarkable influence on the roundness of workpiece especially in boring operation.
Also, the machining head is heavy because it is equipped with many cutting tools, boring tools, etc. in a state of being operable, so that a head-down state is formed when horizontal movement toward the workpiece is repeated. If this state occurs, the clearance between the guide bar and the guide post on the lower side, which is usually about 0.01 to 0.02 mm, is lost, and therefore the guide bar and the guide post are brought into contact with each other when they are fitted to each other, and hence they are worn. As a result, the clearance on the upper side increases, and the machining head lowers relatively, which presents a problem of degraded machining accuracy of workpiece.
To solve such problems, the applicant has proposed a system in which a member for locking the guide bar is contracted by hydraulic pressure, and the machining head and a rotary jig for holding a workpiece are integrated (refer to Japanese Patent Laid-Open No. 7-164222, Abstract and FIG. 6).
The hydraulic system disclosed in Japanese Patent Laid-Open No. 7-164222 has a problem in that the structure is complicated in order to prevent hydraulic fluid from leaking although the effect is high.